Cellular immunity in humans is usually assessed in vitro by the use of plant extracts which act as mitogens (PHA, Con-A, PWM). Assessment of specific cellular immunity to bacteria has been limited to a few bacterial soluble extracts available, but is of considerable interest for many immunologic, clinical and public health problems. In the last year, we succeeded in preparing whole cell bacterial antigens (not extracts from different bacteria including Streptococcus, Staphylococcus aureus, Haemophilus influenzae and Pseudomonas aeruginosa. These antigens made it possible to detect a specific defect in the in vitro lymphocyte response to pseudomonas in cystic fibrosis patients in poor clinical condition. Further understanding of the nature, biologic significance, and development of the in vitro cellular responses to bacteria is needed. The objective of the proposed project are: 1). To gain an understanding of the nature of the in vitro responses of human lymphocytes to killed bacteria. The basic method to be applied is the in vitro lymphocyte response (proliferation) measured by tritiated thymidine incorporation. Whole cell bacteria will be used as antigens (and/or mitogens). Variations of bacteria concentration, incubation time, cell population (T- and B-lymphocytes and macrophages) and plasma fractions will be tested for this purpose. 2). To evaluate the biologic significance of these responses: Two functions have been selected for study: a) induction of in vitro biosynthesis of immunoglobulins, as determined by radioimmunoassay, and b) secretion of lymphokines into culture supernatants as determined by human leukocyte migration inhibition. 3). Assessment of the qualitative and quantitative aspects of the responses in newborns (cord blood) and normal adults: After characterization in adults, some of the methods and variables described above will be applied comparatively to both normal adults and term newborns.